Jimmy Clausen appeared to be fine after taking a brutal helmet-to-helmet hit. Getty Images Chicago Bears quarterback Jimmy Clausen will miss the final game of the season after suffering a concussion on the last drive of the team's loss to the Detroit Lions according to the Chicago Tribune.

While the NFL has done a lot to protect players from concussions, this particular injury is the perfect example of just how scary the NFL's crisis can be and how there is only so much they can do.

Unlike players who show seemingly obvious signs of a concussion following a hit to the head, Clausen popped right up and got into the face of Ezekiel Ansah who delivered the blow. Clausen was never unconscious. He didn't have any trouble standing or walking. He didn't appear woozy and didn't look like he was going to be sick.

Clausen had just taken one of the nastiest helmet-to-helmet hits you will see and he stayed in the game without having been treated or examined by team doctors.

The NFL has gotten better at identifying players who have suffered concussions and making sure they are protected from making the injury worse. But even on the nastiest of hits a concussion may not present itself in an obvious fashion.

Concussions are one thing. Undetectable concussions are something else entirely and something that the NFL needs to be worried about.